كليدواژه :
انتقال اصطكاك , پيش فشار , چسبندگي , ملاتر
چكيده فارسي :
با توجه به آسيب هاي وارده به سازه‌هاي بتني كه ممكن است به دليل عوامل مختلفي پديد آيد، موادي براي تعمير و تقويت اين سازه‌ها مورد نياز است. معمولاً براي ترميم و تعمير سازه هاي بتني از ملات‌هاي پايه سيماني استفاده مي‌گردد. جمع شدگي و تراكم نامناسب ملات هاي تعميري مي تواند باعث كاهش مقاومت چسبندگي بين ملات و بستر بتني گردد. فصل مشترك ملات و بستر داراي اهميت فراواني مي باشد، زيرا عدم تراكم مناسب باعث ايجاد حفرات ريز بين سطح مشترك شده و يكي از عوامل اصلي در كاهش مقاومت چسبندگي مي باشد. لذا در اين تحقيق با اعمال پيش فشارهاي متفاوت روي ملات تعميري، تاثير آن بر مقاومت چسبندگي برشي و كششي بين ملات تعميري و بستر بتني با استفاده از آزمون هاي "انتقال اصطكاك" و "كشيدن از سطح" مورد بررسي قرار گرفته است. براي ساخت ملات هاي تعميري از نسبت سيمان به ماسه برابر 1 به 3 و نسبت آب به سيمان نيز برابر 0.5 استفاده شده است. همچنين تاثير عمل آوري بر كاهش جمع شدگي ملات ها ارائه گرديده است. در ادامه نيز براي ارزيابي مقاومت فشاري درجاي ملات هاي سيماني از آزمون هاي نيمه مخرب "انتقال اصطكاك" و "كشيدن از سطح" استفاده شده و با اندازه گيري ضريب همبستگي و رسم نمودارهاي كاليبراسيون، معادلات تبديل قرائت هاي حاصل از آزمون هاي نيمه مخرب به مقاومت فشاري ملات ها ارائه شده است. در انتها نيز با استفاده از نرم افزار اجزا محدود ABAQUS ترك¬ها و تنش¬هاي بوجود آمده در نمونه ها ارائه شدند. نتايج حاصله بيانگر اين مي باشد كه اعمال فشار 0.5 كيلوگرم بر سانتي مربع باعث افزايش مقاومت چسبندگي برشي و كششي بين لايه تعميري و بتني در سن 90 روز به ترتيب برابر 30.1% 31.4% درصد گرديده است. با استفاده از معادلات y=10x-0.805 و y=17.32x+1.83 به ترتيب مي توان با جايگذاري نتايج حاصل از آزمون هاي "انتقال اصطكاك" و "كشيدن از سطح" در معادله به جاي عبارت x، مقاومت فشاري ملات تعميري را تعيين نمود
چكيده لاتين :
Given the damages to concrete structures caused by different factors, some materials should be used to repair
and strengthen them. In general, cement-based mortars are used to repair concrete structures. The shrinkage
and inappropriate compaction of repair mortars can reduce the bond strength between mortar and concrete
substrate. the shrinkage is an important problem that has an adverse effect on the adhesion between repair
mortar and concrete substrate. The shrinkage can create tensile stress inside mortars, leading to cracking due
to their low tensile strength. The mortar-substrate interface is of great importance since the improper
compaction can create fine pores and lower the bond strength.The suitable compaction of repair mortar while
applying it on the concrete substrate is an effective factor in increasing the adhesion between the mortar and
concrete. The mortar-substrate interface is of great importance since the improper compaction can create fine
pores and lower the bond strength. Therefore, in this study, different prestresses were imposed on repair mortar
to evaluate their effects on the shear and tensile bond strength between repair mortar and concrete substrate
using friction-transfer and pull-off tests. The role of curing in reducing the shrinkage of mortars was also
evaluated. The semi-destructive friction-transfer and pull-off tests were then used to assess the in-situ
compressive strength of cement-based mortars. By calculating the correlation coefficient and plotting the
calibration curves, relationships were provided to convert the measurements obtained from the semidestructive tests to the compressive strength of the mortars. Eventually, the cracks and stresses that appeared
in the specimens were presented using finite element ABAQUS software. The obtained results indicated the
effect of prestress on increasing the shear and tensile bond strength between the concrete substrate and repair
layers. Moreover, a high correlation coefficient was found between the measurements of the in-situ and
laboratory tests. A good agreement was also observed between the finite element modeling and the
experimental results. In some researches, friction transfer and pull-off tests have been used to compare the
compressive strength of fiber-reinforced mortars and polymer-modified mortars with the results of the above
tests, which has resulted in a very high correlation coefficient between the results.
Imposing a prestress of 0.5 kg/cm2
resulted in an increase of 30.1% and 31.4%, respectively, in the shear and
tensile bond strength between the repair mortar and the concrete substrate at the age of 90 days. Imposing a
prestress of 0.1 kg/cm2
resulted in an increase by 7.5% and 5.8%, respectively, in the shear and tensile bond
strength between the repair mortar and the concrete substrate at the age of 90 days. Keeping the specimen in
the free space resulted in 64% more shrinkage compared to the one cured in water. The friction-transfer and
pull-off test results had a correlation coefficient of more than 0.98 with the repair mortar's compressive
strength. Therefore, these tests can be used to evaluate the in-situ compressive strength of mortars. The
compressive strength of repair mortar can be calculated by substituting x for the friction-transfer and pull-off
test results, respectively, in the equations y=10x-0.805 and y=17.32x+1.83
